1. Field of the Invention
This invention relates to a color killer adjustment device used in a TV receiver, specifically to a color killer adjustment device suitable for a configuration in which a CPU (a microcomputer) and a TV signal processing IC are combined, or integrated into a single chip.
2. Description of the Related Art
A TV receiver has a color killer function which intentionally switches off a color signal when the reception is poor due to weak airwaves or the like. To be more specific, a color burst signal in the color signal is converted to a DC (direct current) voltage by smoothing it. And the converted DC voltage is compared with a reference voltage. The color signal is used when the converted DC voltage is larger than the reference voltage. The color signal is forbidden when the converted DC voltage is smaller than the reference voltage. A clear picture is obtained as a result.
A level of the color burst signal at which the color killer function is to be enabled varies depending on each model of the TV receiver, a place of destination, designer's requirement and so on. With this being the situation, the reference voltage is conventionally made adjustable from outside the terminals of the TV signal processing IC. By doing so, an onset point of the color killer function can be freely determined by design of an external circuit of the TV signal processing IC.
However, the method to determine the onset point of the color killer function by design of the external circuit requires physical work to change external parts and their component values which vary from one model to another. Therefore, an alternative method to adjust the onset point of the color killer function without requiring such work has been sought for.